24 October 2013
Researchers at the University of Loughborough have designed and fabricated a flexible radiofrequency connector for the emerging textile electronics industry. They have achieved excellent insertion loss using a hook and loop system, which would allow the wearer to remove components easily and safely.
There has already been a considerable amount of research conducted in the field of textile and wearable electronics. A large number of fabric-based antennas and transmission lines have been developed and refined. However, there has been a noticeable lack of research into how to connect these systems to other electronics and hardware.
These textile systems will, ideally, be integrated into clothing, and as a consequence, need to be either robust to cleaning (able to withstand not only water but also higher temperatures and chemical treatments) or they will need to be removable.
To this end, the Loughborough group manufactured a connector using a hook and loop fastening mechanism. As shown in the image above, the microstrip lines are attached to a number of small hooks using a conductive epoxy. The gapped lines are then bridged by the loop part, and the whole thing can be attached to transmission lines through conducting yarn.
The group have already improved this system by electroplating both hook and loop parts, which very effectively increases the conductivity while maintaining a low insertion loss.
The work described in their Letter is part of a wider project – funded by the Innovative Electronics Manufacturing Research Centre (IeMRC) – called ‘High Performance Flexible, Fabric Electronics for MegaHertz Frequency Communications’. Rob Sieger, one of the authors of the research, explained that “it is a collaborative project, funded by the IeMRC, involving Nottingham Trent University and a number of industrial concerns, the largest of these being Cash’s, a major supplier of security in garment labels worldwide.”
As mentioned above, the main thrust of the research has been into embroidered antennas, as Sieger described: “Embroidery is an attractive manufacturing route as items can be mass manufactured by automated machines; be aesthetically integrated into the clothing – not feeling like something stuck on as an afterthought and negates the need for glue and additional manufacturing processes.” Consequently, the project has involved reviewing a number of different conductive fibres to assess their electrical properties, their mechanical properties and their suitability for commercial embroidery machines.
The field of wearable electronics has continued its growth and remains, as explained by Dr Sieger, a “vibrant area in both academia and industry as was evidenced by the outstanding innovations at the Wearable Technologies Conference in San Francisco this summer.” He then told us that “it is estimated that there will be 50 billion devices connected to the internet by 2020. Establishing textile antennas is a key part of that to enhance user comfort and functionality as well as the aesthetics of the product. It should be noted that major players such as Google and Samsung are reporting ambitious plans for wearable systems.”
The advantages and applications for wearable communication systems are clear, due to their increased size. “Wearable antennas can be used in conjunction with consumer electronics in the 1 to 6GHz spectra,” said Sieger, “however, the advantages of textile antennas increase in the megahertz frequency range where the antennas need to be larger. These cannot be easily incorporated into existing devices without compromising the performance but do not inconvenience the user if they are part of the clothing.” Based on these considerations, he said, “pertinent applications include remote monitoring and communication between fire-fighters; police; military personnel; search and rescue applications or tracking of elderly patients with dementia.”
While working on this project, researchers have been inspired to investigate other, related subjects. These have, according to Sieger, included knitted antennas, textile frequency selective surfaces, inkjet printed antennas on textiles, aesthetic and logo shaped antennas, and other textile interconnects.
The project has been a success for all of the research groups involved, and has proved vital in moving technology towards a completely fabric antenna system. How to evolve the results of the technology is the new concern for the Loughborough group: “We are close to the end of the IeMRC project and feel we have an enabling technology that needs a number of applications to allow us to develop it further,” said Sieger. For example, he explained that “health care, sensing and search and rescue are three possible application areas, and we are currently exploring these, and others, to move the project forward.”
This article is based on the Letter: ‘Flexible radio frequency connectors for textile electronics’ (new window).
A PDF version (new window) of this feature article is also available.
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